Construction of insulating glass units (IGU's) generally involves forming a spacer frame by roll-forming a flat metal strip, into an elongated hollow rectangular tube or “U” shaped channel. Generally, a desiccant material is placed within the rectangular tube or channel, and some provisions are made for the desiccant to come into fluid communication with or otherwise affect the interior space of the insulated glass unit. The elongated tube or channel is notched to allow the channel to be formed into a rectangular frame. Generally, a sealant is applied to the outer three sides of the spacer frame in order to bond a pair of glass panes to either opposite side of the spacer frame. Existing heated sealants include hot melts and dual seal equivalents (DSE). The pair of glass panes are positioned on the spacer frame to form a pre-pressed insulating glass unit. Generally, the pre-pressed insulating glass unit is passed through an IGU oven to melt or activate the sealant. The pre-pressed insulating glass unit is then passed through a press that applies pressure to the glass and sealant and compresses the IGU to a selected pressed unit thickness.
Manufacturers may produce IGUs having a variety of different glass types, different glass thicknesses and different overall IGU thicknesses. The amount of heat required to melt the sealant of an IGU varies with the type of glass used for each pane of the IGU. Thicker glass panes and glass panes having low-E coatings have lower transmittance (higher opacities) than a thinner or clear glass pane. (opacity is inversely proportional to transmittance). Less energy passes through a pane of an IGU having a high reflectance and low transmittance. As a result, more energy is required to heat the sealant of an IGU with panes that have higher reflectance and lower transmittance. For example, less energy is required to heat the sealant of an IGU with two panes of clear, single strength glass than is required to heat the sealant of an IGU with one pane of clear, double strength glass and one pane of low-E coated double strength glass.
Typically, manufacturers of insulating glass units reduce the speed at which the insulating glass units pass through the IGU oven to the speed required to heat the sealant of a “worst case” IGU. This slower speed increases the dosage of exposure. In addition to the line speed sacrificed, many of the IGU's are overheated at the surface, resulting in longer required cooling times, and more work in process.
Some manufacturers produce IGUs in small groups that correspond to a particular job or house. As a result, these manufacturers frequently adjust the spacing between rollers of the press to press IGUs having different thicknesses. The thickness of the IGU being pressed is typically entered manually. Other manufacturers batch larger groups of IGUs together by thickness to reduce the frequency at which spacing between the rollers of the press needs to be adjusted.
There is a need for a method and apparatus for heating sealant of an IGU that automatically varies the energy applied to the IGU based on an optical property of the IGU. In addition, there is a need for a method and apparatus that automatically sets the spacing between press rollers for an IGU being pressed. This type of functionality can provide just in time one piece flow production resulting in constant speed, less manual intervention and more consistency in the process.